This study focusing on build-up and designing a fluorimeter flow injection system with assistance of a 3D printer.. The fluorimeter as new detector in our laboratory is a very simple fluorimeter was designed and built-up by the aid of a 3D printer to housing in which all the components are supplied from the local market. It consists of three major parts. Firstly, a simple, low-voltages, and long-lived light-emitting diodes (LED) with 0.25 watt. The second parts is 450 µL flow cell QS Hellman with four faces in order to select precisely the 90 ₒ angle between the source and third components, the LED arrays detector . All these components were put in small plastic box which the internal and external covers were made from black plastic which thought to prevents the unwanted light from reaching the detector. The device is very light weight (165.5 g ) and the fluorimeter box dimensions were 11cm in length , 8cm in width and 3cm in height.Two Microcontrollers Mega and UNO types were used as data a data-logger and controlled the home-made mini peristaltic pump, respectively. A direct fluorimetric determination of fluorescein dye as an example which was carried out in this work. This thought will be made the construction system a very simple fluorimeter since the dye excited and fluorescent in the visible range.Linearity was found in the range ( 0.2-1.6 x 10- 4mol/L) with a regression coefficient of eight points was 0.9989, r.s.d% for ten replicates of was 0.84% and detection limit was 0.1×10-4mol/L. The sample throughput was 200 samples per hour. The dispersion coefficient of the manifold was 1.04. The lab-build semi-automated fluorometeric FI system was reliable, fast and low cost which is matching our undergraduate laboratories with low budget.